On Seasonal Variation of the 162 kHz Radio Wave Reflection Height: Model Calculations and Their Comparison with Experiments

The seasonal variation of the 162 kHz radio wave reflection height was measured indirectly at Panská Ves using the IPHA method described in Fier and Matys (1992). The fact that these waves are reflected at the height where the electron concentration is about 3.5 × 10 ⁸ m ^–3 was used to model this height using a 1-D model of the lower ionosphere electron concentration described by Ondráková (1993). The comparison of the measurements and model results indicates that: 1. The annual mean of the reflection height derived from measurements is several km higher than that derived from the model; 2. the character of the modelled seasonal variation is different from the real variation shown in Fier and Latovika (1992). The differences are discussed.     

Preliminary Archaeomagnetic Results from a Floor Sequence of a Bread Kiln in Lübeck (Germany)

A sequence of 25 bread-kiln floors was sampled for archaeomagnetic measurements in a bakehouse in the old town of Lübeck, Germany. Due to archaeological dating this kiln floor sequence has been built up presumably from the late 13 ^th to the 18 ^th century. The primary magnetisation component is carried by magnetite (maghemite) and is very stable. Small viscous magnetisation components could be removed easily. The preliminary results of characteristic remanent magnetisation for 23 of the kiln-floor layers show clearly the trend of the geomagnetic secular variation expected for that time interval. By comparison with French and British master curves, the kiln-floor sequence started around 1425 and lasted until 1775 AD. Presently, confidence circles are relatively large and need refineing by measuring more samples, which have already been collected. Together with ¹⁴ C dating that can be determined from the charcoals found in the lowest layers and thermoluminescence dating of the layers, we expect to obtain, for the first time, a secular variation curve for Northern Germany covering the time interval from 1400 to 1800 years AD.     

Biogeochemistry of iron in an acidic lake

In this paper, the fate of iron in Lake Cristallina, an acidic lake in the Alps of Switzerland, is discussed. A simple conceptual model is developed in order to explain the observed diel variation in dissolved iron(II) concentration. Biotite weathering provides reduced iron that is oxidized and subsequently precipitated in the lake. The amorphous Fe(III)hydroxide (FeOOH xH₂O), found in the sediments of Lake Cristallina, is an Fe(II) oxidation product. This oxygenation reaction is most probably catalyzed by bacteria surfaces, as indicated by the relatively high estimated oxidation rate compared to the oxidation rate of the homogeneous oxidation of inorganic Fe(II) species at the ambient pH of Lake Cristallina (pH 5.4 at 4 °C) and by the scanning electron micrograph pictures. Under the influence of light, these amorphous iron(III)hydroxide phases are reductively dissolved. The net concentration of Fe(II) reflects the balance of the reductive dissolution and the oxidation/precipitation reactions and tends to parallel the light intensity, leading to a diurnal variation in the Fe(II) concentration. The rate of the photochemical reductive dissolution of Lake Cristallina iron(III)hydroxides is greatly enhanced in situ and in the laboratory by addition of oxalate to the lake water.     

Induction, adaptation and recovery of biological responses: implications for environmental monitoring

A wide range of biological responses have been used to identify exposure to contaminants, monitor spatial and temporal changes in contamination levels, provide early warning of environmental deterioration and indicate occurrences of adverse ecological consequences. To be useful in environmental monitoring, a biological response must reflect the environmental stress over time in a quantitative way. We here argue that the time required for initial induction, maximum induction, adaptation and recovery of these stress responses must first be fully understood and considered before they can be used in environmental monitoring, or else erroneous conclusions (both false-negative and false-positive) may be drawn when interpreting results. In this study, data on initial induction, maximum induction, adaptation and recovery of stress responses at various biological hierarchies (i.e., molecular, biochemical, physiological, behavioral, cytological, population and community responses) upon exposure to environmentally relevant levels of contaminants (i.e., metals, oil, polycyclic aromatic hydrocarbons (PAHs), organochlorines, organophosphates, endocrine disruptors) were extracted from 922 papers in the biomarker literature and analyzed. Statistical analyses showed that: (a) many stress responses may decline with time after induction (i.e., adaptation), even if the level of stress remains constant; (b) times for maximum induction and recovery of biochemical responses are positively related; (c) there is no evidence to support the general belief that time for induction of responses at a lower biological hierarchy (i.e., molecular responses and biochemical responses) is shorter than that at higher hierarchy (i.e., physiological, cytological and behavioral responses), although longer recovery time is found for population and community responses; (d) there are significant differences in times required for induction and adaptation of biological responses caused by different types of contaminants; (e) times required for initial and maximum induction of physiological responses in fish are significantly longer than those in crustaceans; and (f) there is a paucity of data on adaptation and recovery of responses, especially those at population and community levels. The above analyses highlight: (1) the limitations and possible erroneous conclusions in the present use of biomarkers in biomonitoring programs, (2) the importance of understanding the details of temporal changes of biological responses before employing them in environmental management, and (3) the suitability of using specific animal groups as bioindicator species.     

IV. Bücher- und Zeitschriftenschau

Ohne Zusammenfassung     

Bücher- und Zeitschriftenschau

Ohne Zusammenfassung     

Junge Krustenbewegungen in den Alpen

Zusammenfassung Junge Krustenbewegungen sind tektonische Vorgänge, die nach Vollendung des strukturellen Baues das Formenstockwerkgebäude verändern. Solche Bewegungen können nur aus den Formen selbst mit zwingender Sicherheit nachgewiesen werden. Der geologische Befund allein erweist die Bewegung nicht als unbedingt jung. Das Hauptargument für eine allgemeine Verbreitung junger Verbiegungen, die angenommenen Einwalmungen der Gipfelflur, basiert auf nicht zutreffenden Voraussetzungen. Auch die beiden klassischen Beispiele junger Krustenbewegungen, die Brennerquerfurche und die Inntallängsfurche sind nicht als solche erweisbar. Mit jungen Krustenbewegungen als Arbeitshypothese ist ganz besondere Vorsicht am Platze.     

Über die Variationen des Ionosphärischen Conversionskoeffizienten nach Schrägeinfallsmessungen im Langwellenbereich

Резюме Крутизна кривых захода и восхода Солнца, отображающаяся в годовом ходе изменений в виде вечернего возрастания или утреннего убывания коэффициента конверсии проявляется весьма неравномерио. Здесь уместно провести параллель с явлениями имеющими место в периоде летних месяцев (март— октябрь), когда переход от дня к ночи и наоборот осуществляется быстро. Годовой ход коэффициента конверсип в периоде от зимы к лету характеризуется возрастанием значений ϱ согласно закону положения Солнца относителяно слояE; такое возрастание весной и осенью прерывается вследствие явлений, связанных с перемещением дрейфующей системы на поверхости отражения. В летних месяцах кривая значений ϱ имеет более низкие явления. Влияние повышенной солнечной возмущающей активности в равноденствиях проявляется в особенности на северном участке (245кец) в виде соответствующего расположения минимумов на кривой изменений. Помимо этого в максимуме солнечных пятен был обнаружен 27 дневный период повторяемости коэффициента конверсии, который отчетливо проявляется в скользящих средних значений ϱ полученных в результате вычислений, осуществленных непрерывно в десятидневных интервалах в течение 1958 г.

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Anschrift: Geophysikalisches Observatorium, Collm über Oschatz, DDR.     

Active oceanic spreading in the northern North Fiji Basin: Results of the NOFI cruise of R/V L'Atalante (newstarmer project)

The South Pandora and the Tripartite Ridges are active spreading centers located in the northern part of the North Fiji Basin. These spreading centers were surveyed over a distance of 750 km during the NOFI cruise of R/V L'Atalante (August–September 1994) which was conducted in the frame of the french-japanese Newstarmer cooperation project. SIMRAD EM12-dual full coverage swath bathymetric and imagery data as well as airgun 6-channel seismic, magnetics and gravity profiles were recorded along and offaxis from 170°40 E to 178° E. Dredging and piston coring were also performed along and off-axis. The axial domain of the South Pandora Ridge is divided into 5 first-order segments characterized by contrasted morphologies. The average width of the active domain is 20 km and corresponds either to bathymetric highs or to deep elongated grabens. The bathymetric highs are volcanic constructions, locally faulted and rifted, which can obstruct totally the axial valley. The grabens show the typical morphology of slow spreading axes, with two steep walls flanking a deep axial valley. Elongated lateral ridges may be present on both sides of the grabens. Numerous volcanoes, up to several kilometers in diameter, occur on both flanks of the South Pandora Ridge. The Tripartite Ridge consists of three main segments showing a sigmoid shape. Major changes in the direction of the active zones are observed at the segment discontinuities. These discontinuities show various geometrical patterns which suggest complex transform relay zones. Preliminary analysis of seismic reflection profiles suggest that the Tripartite Ridge is a very young feature which propagates into an older oceanic domain characterized by a significant sedimentary cover. By contrast, a very thin to absent sedimentary cover is observed about 100 km on both flanks of the South Pandora Ridge active axis. The magnetic anomaly profiles give evidence of long and continuous lineations, parallel to the South Pandora Ridge spreading axis. According to our preliminary interpretation, the spreading rate would have been very low (8 km/m.y. half rate) during the last 7 Ma. The South Pandora and Tripartite Ridges exhibit characteristics typical of active oceanic ridges: (1) a segmented pattern, with segments ranging from 80 to 100 km in length; (2) an axial tectonic and volcanic zone, 10 to 20 km wide; (3) well-organized magnetic lineations, parallel to the active axis; (4) clear signature on the free-air gravity anomaly map. However, no typical transform fault is observed; instead, complex relay zones are separating first-order segments.